1. Field of the Invention
The present invention relates to a W-CDMA wireless base station adapted to perform an optimal channel allocation for example in a CDMA mode wireless communication system including a W-CDMA (Wideband-Code Division Multiple Access) mode.
2. Description of the Related Art
FIG. 10 is a schematic block diagram showing a configuration example of a high frequency section and a base band section in a convention W-CDMA wireless base station. Operations and configurations of the respective high frequency and the base band sections of this convention W-CDMA wireless base station are as follows:
In a transmission operation, a transmission data is modulated via a modulation section 10 and then multiplied by a spread code at a spread section 20 so as to output as a transmission base band signal to the high frequency section 30. The high frequency section 30 converts the transmission base band signal into a transmission high frequency signal to output to an antenna 40. That is, this transmission high frequency signal is transmitted via the antenna 40 outwardly.
In a reception operation, a reception high frequency signal is received by the antenna 40 and outputted to the high frequency section 30. Then, the high frequency section 30 converts the reception high frequency signal into a reception base and signal and then outputs it in parallel to a preamble detection section 50, a path search section 60, a DPCH (Dedicated Physical Channel) demodulation section 70 and RACH (Random Access Channel) demodulation section 80. It should be noted that the DPCH is a separate channel while the RACH is a common channel.
The base band section of the conventional W-CDMA wireless base station generally comprises a plurality of the preamble detection sections 50 and a plurality of the path search sections 60. FIG. 11 is a schematic block diagram showing a configuration example of the conventional base band section comprising the plural preamble detection sections and the plural path search sections. As shown in FIG. 11, there are provided three preamble detection sections 50A–50C for example each having a similar configuration to that of the preamble detection section 50 and three path search sections 60A–60C for example each having a similar configuration to that of the path search section 60.
First of all, the preamble detection section 50 and the path search section 60 will be described with reference to FIGS. 10–12. As shown in FIG. 10, the preamble detection section 50 is comprised of a matched filter 51 and a detection portion 52 while the path search section 6 is comprised if a matched filter 61 and a detection portion 62. FIG. 12 is a schematic block diagram showing a configuration example of a conventional matched filter used as the matched filter 51 or 61. The conventional matched filter, as shown in FIG. 12, is comprised of shift registers 110, multipliers 120 and an adder 130. In this case of FIG. 12, the number of taps is n+1. There are provided n shift registers 110 which are adapted to serially shift an inputted reception base band signal thereover. Also, there are provided n+1 multipliers 120 which are each adapted to perform a multiplication of the reception base band signal which has been shifted serially and outputted from its corresponding tap and a spread code. In addition, the adder 130 is adapted to add outputs from all of the multipliers 120 and output the obtained result as a correlation value.
The matched filter 51 of the preamble detection section 50 performs a correlative operation of the reception base band signal and the spread code For acquiring a preamble of an RACH, and then outputs the result as a correlation value to the detector 52. Then, the detector 52 performs a detection of the preamble by using that correlation value. In this example, a DSP (Digital Signal Processor) is used as the detector 52.
On the other hand, the matched filter 61 of the pat search section 60 performs a correlative operation of the reception base band signal and the spread code for acquiring a path, and then outputs the result as a correlation value to the detector 62. The, the detector 62 performs a detection of the path by using that correlation value. In this example, a DSP (Digital Signal Processor) is used as the detector 56.
Turning again to FIG. 10, the DPCH demodulation section 70 comprises a plurality of fingers 71 and a RAKE portion 72 while the RACH demodulation section 80 comprises a plurality of fingers 81 and a RAKE portion 82. FIG. 13 is a schematic block diagram showing a configuration example of a convention finger 71 or 81. As shown in FIG. 13, the fingers 71 or 81 are each comprised of a multiplier 210 and an integrator 220. The multiplier 210 performs a multiplication of the reception base band signal and a spread code. The integrator 220 integrates outputs from the multiplier 210 and then outputs the result as a correlation value.
According to the output from the path search section 60, a spread code is inputted to each of the plurality of fingers 71 for each path per DPCH. Each finger 71 performs a correlative operation of the inputted spread code and the reception base band signal and then outputs the result as a correlation value to the RAKE portion 72. The RAKE portion 72 combines (or synthesizes) correlation values from the plurality of fingers 71 by using RAKE and demodulates it, thereby outputting the demodulated signal as a reception data.
On the other hand, a spread code is inputted to each of the plurality of fingers 81 for each path per DPCH according to the output from the path search section 60. Each finger 81 performs a correlative operation of the inputted spread code and the reception base band signal and then outputs the result as a correlation value to the RAKE portion 82. The RAKE portion 82 combines correlation values from the plurality of fingers 81 by using RAKE and demodulates it, thereby outputting the demodulated signal as a RACH data.
The high frequency section and the base band section of the conventional W-CDMA wireless base station as described above are designed to perform a channel allocation according to a fixed specification. FIG. 14 is a table showing a specification example of the channel allocation performed in the conventional W-CDMA wireless base station. Namely, the high frequency section and the base band section of the conventional W-CDMA wireless base station is designed to perform the channel allocation according to the fixed specification, for example, as shown in FIG. 14, in which a cell radius is 15 Km, the number of Signatures available for RACH is 8, the number of RACH's are provided for 8 channels and the number of DPCH's are provided for 32 channels.
However, it is desired, upon an actual operation of the W-CDMA wireless base station, to change over the cell radius, the number of Signature and the like depending on the location for installation thereof. Also, the RACH, which is the common channel, is used for a packet communication during few traffic and readily assumed to be often used in a portable telephone equipped with a browser function. It can be assumed that the DPCH having a more traffic such as a high-speed data communication is sometimes occurred. Therefore, it is desired to sufficiently meet change in the numbers of RACH's and/or the DPCH's. In order to overcome these difficulties, it is needed to design a W-CDMA wireless base station capable of meeting every specification. However, such a W-CDMA wireless base station will have to include a significant amount of redundancy and then requires a large scale circuitry.
Hence, in order to address the above-mentioned problems, an object of the present invention is to provide a CDMA wireless base station which is able to meet various specifications over a wide range, i.e., capable of dynamically changing an allocation of the number of RACH's and/or DPCH's depending on the cell radius and the number of Signatures, thereby enabling its circuit scale to be reduced.